Recently, pressed powder magnetic cores, as, for example, in a choke coil, reactor coil, etc., are often adopted in an environment where the choke coil, reactor coil, etc., are used under a high current, or where they are used in a high-frequency range or in a limited space. So, also the soft magnetic powder that is used for such a choke coil, reactor coil, etc., must have superior soft magnetic property if it may be used under a high current, or at a higher frequency, or will be suitably used in a choke coil, reactor, coil, etc., that have limited sizes.
In general, soft magnetic powder that is used as a pressed powder magnetic core should have a high saturation magnetic flux density, high magnetic permeability, and a low core loss, because the pressed powder magnetic cores are often used under a high current. Also, it is preferred that the core be highly resistive in light of achieving a low current loss.
However, usually it is difficult to manufacture a soft magnetic powder that has all these characteristics. So, depending on the need, different soft magnetic powders are used, such as a) an oxidized soft magnetic powder (Ferrite), b) amorphous Fe-group-based soft magnetic powder, and c) crystalline Fe-group-based soft magnetic powder (Metal Alloy) (for example, see Patent Documents 1 and 2).    a) The oxidized soft magnetic powder is highly-resistive and thus has a low core loss. But it is unsuitable for use under a high current because it has a low saturation magnetic flux density.    b) Amorphous Fe-group-based soft magnetic powder has a superior magnetic property. But due to the structure of the powder composition the amorphous Fe-group-based soft magnetic powder has very high hardness of the powder and it is hard to press it into a desired shape. Also, it does not have a sufficient saturation magnetic flux density, so that it cannot be used as a pressed powder magnetic core of a small size.    c) Crystalline Fe-group-based soft magnetic powder has a high saturation magnetic flux density and also has comparatively lower hardness of the powder. So, it can be pressed into a powder magnetic core having a low core loss if insulation of the surface of the powder is secured, for example, by using resin, etc. Also, it is suitable for use as a pressed powder magnetic core of a small size that is used under a high current and in a high-frequency range.
It is generally recognized that finer Fe-group-based alloy soft magnetic powder is suitably used in an environment of a high-frequency range or for obtaining a low core loss.
However, it needs a higher level of technology to press finer powder into a desired shape or it needs more resin, etc., to obtain a sufficient insulation between the fine powders. For this reason there is a problem in that the high permeability property (magnetic property) that the Fe-group-based alloy soft magnetic powder itself normally has cannot be utilized because of the lowering of the magnetic permeability of the pressed powder magnetic core itself due to a decrease in the density of the pressed powder magnetic core. Patent Documents 1 and 2 disclose coating the surface of the powder by oxidation. But the coating by oxidizing makes the manufacturing process complex.
For these reasons, even by using the conventional Fe-group-based soft magnetic powder, if higher magnetic permeability is obtained without increasing the core loss, the pressed powder magnetic core that has lower density can be used under a high current or in a high-frequency range. Thus minimizing the size of the pressed powder magnetic core and lowering the core loss can be achieved without using a high-level pressing technology.
Patent Documents 1 and 2 disclose manufacturing the soft magnetic powder by a water atomizing process, etc., as in the present invention. They disclose using an adjunct component selected from Si, Al, and Cr and also disclose that it is possible to add the metals of groups IV-VI as a small-amount adjunct component (Patent Document 1, Paragraph 0053, and Patent Document 2, Paragraphs 0021 and 0044). But the metals of groups IV-VI as small-amount adjunct components (transition metals whose d-orbitals are less than half filled) are shown as mere examples, just as are Mn, Co, Ni, Cu, Ga, Ge, Ru, Rh, etc., of the metals of groups VII-XI (transition metals whose d-orbitals are more than half filled) and just as is B (boron). Further, neither Patent Document 1 nor 2 includes any description that implies that the small-amount adjunct component should be added to improve the magnetic property (particularly to attain the high magnetic permeability) (Patent Document 1, Paragraph 0053, and Patent Document 2, Paragraph 0044). Paragraph 0044 of Patent Document 2 says that the small-amount adjunct component that is added is preferably 1 wt % or less.
Although it does not affect the patentability of the present invention, there are the prior-art publications, i.e., Patent Documents 3-5, that refer to the amorphous Fe-group-based soft magnetic powder, to which a small amount of the metals of groups IV-VI is added.
The metals of groups IV-VI denoted by M in the compositional formula Fe100-a-b-x-y-z-w-tCOaNibMxPyCzBwSit of Patent Document 3 are shown as mere examples, like Pd, Pt, Au, etc., of the metals of groups X-XI given in Patent Documents 1 and 2. Further, in Patent Document 3 the metals of groups IV-VI are added to improve the corrosion resistance of the powder by a passivated oxide coating being formed (Paragraph 0024). Also, the description in that paragraph stating that “the amount of M that is added is preferably 0-3 atom % if the magnetic property and corrosion resistance are considered” should mean, when the preceding paragraph is considered, that Nb does not increase the magnetic property, but that rather it would cause the magnetic property to be lowered if it were added in a large amount.
The metals of groups IV-VI denoted by M′ in the compositional formula T100-x-yRxMyM′z of Patent Document 4 are shown as mere examples, like the other metals of groups VII-XI, and further, like non-metals or typical metals like P, Al, Sb, etc. Also, in Patent Document 4, by adding M′, the corrosion resistance is expected to improve. Also, Patent Document 4 says that the amount to be added is preferably in the range of 0-30%, more preferably 0-20% (Patent Document 4, page 9, the lower part, the second paragraph). That is, the addition of M′ as stated in Patent Document 4 does not suggest that one should add the metals of groups IV-VI in a small amount of 4% or less as is disclosed in the present invention.
Similarly, in Patent Document 5, also the metals of groups IV-VI denoted by M′ in compositional formula T100-x-yRxMyM′z are given only as mere examples, like the metals of groups VII-XI and like the typical metals, such as Zn, Ga, etc.
Paragraph 0032 of Patent Document 5 says, “Addition of element M′ has an effect where the coercive force of a micro-crystallite alloy is lowered. However, if the content of the element M′ is too large, the magnetization is lowered. So, the ratio z of element M′ in the composition should be 0 at %≦z≦10 at %, preferably 0.5 at %≦z≦4 at %.” This statement, like one in Patent Document 3, is considered to imply that element M′ contributes to lowering a core loss by minimizing the coercive force of soft magnetic, but that it does not contribute to increasing the magnetic permeability (magnetization).